Issue
You can read one of the following error messages on your Drupal website
Search API Solr 8.x-1.x is unsupported. Upgrade to 8.x-3.x or newer.or
The support for Search API Solr 8.x-1.x ends 2020-12-31. Ensure to upgrade to 8.x-3.x in combination with the Acquia Search Solr module...or
The support for Search API Solr 8.x-1.x ends 2020-12-31. Ensure to upgrade to 4.x or newer before that date.
Resolution
We recommend that you disregard the message for now, as Acquia will sponsor continued maintenance of the Search API Solr 8.x-1.x module by the Drupal community through 2021, and there should be no danger or problem whatsoever if you continue to use the above mentioned module versions.